The present invention relates to wax compositions comprising wax and oil.
Fully refined petroleum waxes have numerous industrial applications including use in adhesives, candlemaking, food coatings, lubricants, paper coatings and waterproofing.
In a typical sequence of wax production, long residue is subjected to vacuum distillation, leading to spindle oil distillate, light machine oil distillate, medium machine oil distillate and distillation residue as typical products. Such products may be subjected to solvent refining and de-waxing to yield wax products such as spindle oil slack wax (SPO wax), light machine oil slack wax (LMO wax), medium machine oil slack wax (MMO wax) and bright stock slack wax (BSO) wax. These waxes may be treated by re-pulping processes, typically leading to waxes having  greater than 3% w/w oil content, or solvent de-oiling, typically leading to waxes having  less than 1% w/w oil content.
The initial de-waxing stage removes a relatively small proportion of wax from a large proportion of oil. This operation is usually performed by xe2x80x98solvent de-waxingxe2x80x99 in which the waxy feed is mixed with a blend of solvents, chilled to crystallise the wax, and then filtered to remove the wax. At this stage SPO wax, LMO wax, MMO wax and BSO wax fractions usually contain between 10 to 35% w/w oil.
The presence of oil in a petroleum wax has a negative influence on its final properties. As the oil content increases, the tensile strength, hardness and resistance to scuffing are impaired. The oil content of such waxes may cause staining upon contact with paper.
In candlemaking, for example, the presence of excess oil can result in both the candles bending and dripping during use at ambient temperature and also tacking/sticking during storage at room temperature.
In order to mitigate the negative effects that oil impart on the wax, de-waxing is usually followed by an expensive de-oiling step to reduce the oil contents to typical levels of  less than 1% w/w. This is usually achieved by a xe2x80x98solvent de-oilingxe2x80x99 process. Solvent de-oiling is essentially similar to solvent de-waxing but is designed to remove a relatively small amount of oil from a larger proportion of wax. The operation is controlled to produce a wax of the required oil content and melting point. An older xe2x80x98sweatingxe2x80x99 process can be used to de-oil coarsely crystalline paraffin waxes. The sweating process results in a crude fractionation of the wax components wherein lower melting point waxes are removed along with the oil.
The Foots oil (approximately 12-20% w/w) that results from such de-oiling processes is normally sent to a catcracker. Hence solvent de-oiling is both a costly and wasteful process.
The tendency of a wax to xe2x80x98bleedxe2x80x99 or sweat oil can be evaluated by determining its bleeding number. Tests for assessing the bleeding number of petroleum waxes are known in the art and are described, for example, in Petroleum Refiner, 1948, Vol. 27, No. 8, pp429-431.
It is highly desirable to be able to produce waxes that do not xe2x80x98bleedxe2x80x99 or sweat oil, without having to employ the full de-oiling process.
The present invention provides a method for reducing the bleeding number of wax compositions comprising wax and oil, wherein said waxes are selected from petroleum and synthetic waxes and said oil is present in the range of 1 to 45 percent by weight (% w/w), by incorporating in the composition an effective amount of an oil retention agent in the form of an elastomeric polymer. The invention has particularly useful application to wax compositions used for wax candles. The invention further provides the use of elastomeric polymers for reducing bleeding number in wax compositions.
The present invention provides a method for reducing bleeding number in petroleum and synthetic wax compositions containing wax and oil, wherein an oil retention agent in the form of an elastomeric polymer is incorporated in the composition. The incorporation of elastomeric polymer makes it feasible to avoid having to fully de-oil the wax prior to use, depending upon the bleeding tendency required in the composition.
Examples of waxes that can be treated by the invention are paraffin waxes and paraffin wax blends, preferably SPO, LMO, MMO and BSO waxes.
The process can be equally applied to synthetic waxes, such as Fischer-Tropsch (FT) waxes. Said FT waxes are hydrocarbon waxes that are produced by the reaction of carbon monoxide and hydrogen in the presence of a catalyst.
Petroleum and synthetic waxes that may be conveniently treated by the present invention preferably have an oil content in the range of from 1 to 35% w/w and most preferably in the range of from 1.5 to 15% w/w.
Elastomeric polymers are generally associated with polymers of conjugated dienes, such as butadiene or isoprene, or with copolymers of conjugated dienes with another copolymerisable monomer for example a mono vinyl aromatic hydrocarbon, such as styrene. It is emphasised that the elastomeric polymer used in the present invention is not restricted to such polymers or copolymers and may include any polymer with elastomeric (i.e. rubbery) properties. Suitable elastomeric polymers include elastomeric polymers of olefins, diolefins and cyclic olefins amongst others those that have been produced using metallocene catalysts (metallocene polymers). However, the polymers of conjugated dienes, or copolymers of dienes are the preferred elastomeric polymers in respect of this invention. These polymers may be random and/or block copolymers.
The preferred elastomeric polymers in respect of this invention are block copolymers of at least one mono vinyl aromatic monomer and at least one conjugated diene. More preferably, the block copolymer contains at least one predominantly poly(mono vinyl aromatic) block and at least one predominantly poly(conjugated) diene block. Optionally, the poly(conjugated diene) block may be completely, partially or selectively hydrogenated.
With the term xe2x80x9cpredominantlyxe2x80x9d is meant that the main monomer of the respective individual blocks optionally may be mixed with minor amounts (e.g. amounts less than 50% mol/mol) of another comonomer and more in particular with minor amounts of the main monomer of other blocks.
Examples of the mono vinyl aromatic monomers may be selected from styrene, xcex1-methylstyrene, p-methylstyrene, m-methylstyrene, o-methylstyrene, p-tert-butylstyrene, dimethylstyrene, and various other alkyl-substituted styrenes, alkoxy-substituted styrenes vinylnaphthalene and vinyl xylene. The alkyl and alkoxy groups of the alkyl-substituted or alkoxy substituted styrenes respectively preferably contain from 1 to 6 carbon atoms, preferably from 1 to 4 carbon atoms. The conjugated diene monomers are preferably conjugated dienes with from 4 to 8 carbon atoms per monomer, for example, butadiene, isoprene, 2-ethyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 1,3-butadiene, 1,3-pentadiene, 2,4-hexadiene, 3-ethyl-1,3-pentadiene, and mixtures thereof.
Of these monomers styrene is the preferred vinyl aromatic monomer. Butadiene or isoprene or mixtures thereof are the preferred conjugated dienes. Block copolymers which contain only substantially pure poly(butadiene) or pure poly(isoprene) blocks are particularly preferred.
The apparent molecular weight of the elastomeric polymer may conveniently be in the range of from 20,000 to 750,000 and preferably in the range of from 40,000 to 730,000 and more preferably in the range of from 60,000 to 700,000.
With the term xe2x80x9capparent molecular weightxe2x80x9d as used throughout the specification is meant the molecular weight of a polymer, as measured with gel permeation chromatography (GPC) using poly(styrene) calibration standards (according to ASTM D 3536).
The elastomeric block copolymers may be linear triblock or multiblock copolymers or multi-armed or star shaped symmetrical or unsymmetrical block copolymers. Diblock copolymers may also be used, as well as mixtures of block copolymers such as triblock copolymers containing diblock copolymers.
The elastomeric block copolymers, which are incorporated in wax compositions described herein, may be prepared by any method known in the art including the well known full sequential polymerisation method, optionally in combination with reinitiation, and a coupling method, as illustrated in e.g. U.S. Pat. No. 3,231,635; U.S. Pat. No. 3,251,905; U.S. Pat. No. 3,390,207; U.S. Pat. No. 3,598,887; U.S. Pat. No. 4,219,627; EP-A-0,413,294; EP-A-0,387,671; EP-A-0,636,654; and WO 04/22931, all of which are herein incorporated by reference. Examples of coupling agents used in this coupling method are, for example, dibromoethane, silicon tetrachloride, diethyl adipate, divinylbenzene, dimethyldichlorosilane, methyl-dichlorosilane. Particularly preferred in such a preparation route is the use of non-halogen containing coupling agents, for example gamma-glycidoxypropyl-trimethoxysilane, and diglycidylether of bisphenol A (EPON(copyright) 825 resin).
The vinyl aromatic monomer content of the elastomeric polymer is preferably in the range of from 0 to 70% w/w, more preferably from above 0 to 50% w/w.
As indicated above, the elastomeric polymer may and indeed preferably is a hydrogenated block copolymer. The elastomeric polymer may be hydrogenated by any suitable technique. The hydrogenation may be complete or partial. In addition, it is possible to selectively hydrogenate just the non-aromatic (i.e. ethylenic) unsaturation so as to convert, e.g. a polyisoprene block to an ethylene propylene rubber (EPR) block.
The poly(conjugated diene) blocks can be hydrogenated up to a substantial degree, i.e. more than 80% of the original ethylenic unsaturation has been hydrogenated. According to the preferred embodiment of the present invention, the poly(conjugated diene) blocks have been hydrogenated up to a residual ethylenic unsaturation (RU) of at most 10%, and most preferably less than 5%.
Examples of elastomeric polymers which can be conveniently used in the present invention include elastomeric block copolymers sold under the trademarks KRATON(copyright) D and G polymers, preferably KRATON(copyright) elastomeric block polymers sold under the trade designations of KRATON(copyright) D1102, G1650, G1652, G1654, G1657, G1726, G1750, and G1780 polymers are used. Suitable metallocene polymers that may be used in the course of the present invention include those sold under the trade designations ENGAGE(copyright) 8200 and EXACT(copyright) 4049 polymers.
It will be appreciated that mixtures of elastomeric polymers may also be incorporated in the wax composition.
For cost reasons, the amount of elastomeric polymer incorporated in the wax composition in order to reduce bleeding number will generally be kept as low as possible. The amount of elastomeric polymer incorporated in the wax composition is preferably in the range of from 0.1 to 10% w/w, and more preferably in the range of from 0.1 to 5% w/w based on wax composition.
The incorporation of elastomeric polymer in the wax composition is preferably in an amount such as to reduce the bleeding number of the wax composition by at least 10%, preferably at least 30% and more preferably at least 50%, measured at a temperature of generally at least 30xc2x0 C., preferably at least 35xc2x0 C., more preferably at least 40xc2x0 C. and most preferably at least 45xc2x0 C. Most preferably, the elastomeric polymer is incorporated in an amount sufficient to reduce the bleeding number of the wax composition to generally less than 8 mm, preferably less than 6 mm, more preferably less than 2 mm and most preferably 0 mm, measured at a temperature of generally at least 30xc2x0 C., preferably at least 35xc2x0 C., more preferably at least 40xc2x0 C. and most preferably at least 45xc2x0 C. Moreover, the incorporation of elastomeric polymers in wax compositions can significantly increase the hardness of the waxes produced.
Incorporation of the elastomeric polymer in the wax composition is preferably done in a manner which achieves a homogeneous or substantially homogeneous incorporation of the polymer into the wax. This may conveniently be achieved by physical blending.
Blending of elastomeric polymers into wax compositions requires the combination of a suitable degree of shear at a suitable temperature. As the amount of elastomeric polymer present in the composition will be low, the temperature is the most significant parameter. But, to reduce the blending time it is necessary to apply some mechanical shear. Thus, temperature is the more significant parameter and little or no mechanical shear may be necessary.
This minimum operating temperature is strongly related to the molecular weight of the wax and that of the elastomeric polymer; in particular that of the polystyrene end-block when a polystyrene-containing block copolymer is used. The temperature will usually be the maximum temperature the wax can withstand with a maximum of 250xc2x0 C. As an example, a 30xc2x0 C. wax, that is to say a wax with a melting point of 30xc2x0 C., will require 120xc2x0 C. with a low molecular weight elastomeric polymer and 190xc2x0 C. with a high molecular weight elastomeric polymer.
The use of a high shear mixer makes it possible to work at temperature slightly lower than usually needed for a conventional mixer.
For instance, the modification of the wax may be performed with a high shear rotor/stator mixer equipment. Many other techniques may also be employed to provide a homogeneous wax/elastomeric polymer composition, including but not limited to the use of internal mixer, Z-blade and extruder (screw has to be designed for super low viscosities) equipment.
Wax compositions described in the present invention can be conveniently used in a wide range of applications. The present invention can be suitably employed in traditional wax applications wherein oil retention is an important feature of use. Use of wax compositions provided by the present invention includes candles, adhesives, dipping, carbon papers, crayons, dental modelling, food coating, matches, packaging material, polishes, electrical specialities, metal casting, moisture resistance, binders and metal injection moulding.
The wax composition can be further combined with other additives including but not limited to stearic acid, mould releases, colourants, dyes, odourants, UV inhibitors, modifiers and hardening resins.
In a preferred embodiment of the invention said compositions are employed in the production of wax candles.
Candles are typically made by casting, compression, dipping, drawing, extrusion, moulding, pouring or rolling processes. Household candles are usually made by moulding processes.
Wax candles produced according to the present invention can be dip-coated with a higher melting point wax in order to reduce dripping.
The present invention can be applied to the production of all types of wax candles, including for example church candles, shaped decorative candles, porch light lantern candles and night lights.
The invention is illustrated by the following examples, which should not be regarded as limiting the scope of the invention in any way.